This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The number of non-ribosomal derived cyclic peptides isolated from marine sources continues to grow. Such peptides are relatively stable toward enzymatic degradation and, in being less polar, are more biologically available than the linear type. Proline-rich cyclopeptides constitute a relatively new class. Most members of this group are sponge-derived hepta- or octapeptides with non-polar amino acid residues (usually with one or two aromatic representatives) interspersed among the proline units. Examples include the axinellins, axinastatins, hymenamides, phakellistatins, stylisins, stylissamides, stylopeptide wainunuamide, and dominicin. Phakellistatins 7-9 and 12 are examples of proline-rich cyclic decapeptides. We have now reported the isolation and characterization of a new proline-type decapeptide, stylopeptide 2, obtained from the same collection of the marine sponge Stylotella sp. that provided stylopeptide 17 and stylostatin 1.11